1. Field of the Invention
The present invention relates to cycling distributor valves with free valve plungers, and more particularly to multiple-plunger distributor valves for the supply of lubricant at different rates to a number of destination points, in accordance with the progressive cycling operation of the valve plungers.
2. Description of the Prior Art
Progressive distributor valves of the above-mentioned type are primarily used in conjunction with the supply of lubrication oil or grease from a central pressure lubrication unit to a number of separate points of lubrication or to subsidiary distributor valves. This kind of progressive distributor valve may also be used in connection with other applications, where a common supply of a pressurized medium is to be subdivided into a plurality of separate branch flows and where the rate at which the medium is fed into the separate branches is to be different from branch to branch.
A progressive distributor valve achieves this by virtue of its cycling operation which involves several, i.e. at least three, free valve plungers, each being usually accommodated inside a separate valve segment, the valve segments being combined into a compact valve block assembly. Each valve plunger, by executing a reciprocating motion of fixed stroke length inside its bore, discharges lubricant alternatingly to two branch lines, the quantity involved being determined by the plunger diameter and by its stroke. The plunger also performs a control function for the next-following plunger, as soon as it reaches an end position. For this reason, it is necessary that the plunger strokes remain constant and are not adjustable for a possible adjustment of the quantities of lubricant supplied to the branch lines. These restrictions apply generally to all conventional progressive distributor valves, as well as to parallel-controlled progressive distributor valves.
Accordingly, it remains a major problem with all progressive distributor valves to obtain some sort of adjustability for the quantities of lubricant which are discharged into the branch lines. In most cases, the determination of the quantities supplied to the branch lines can only be made by accordingly sizing the diameter of each valve plunger. The prior art in this field therefore includes distributor valves having several valve plungers of unequal diameter for the supply of different quantities of lubricant to the corresponding branch lines.
Also known from the prior art are attempts to adjust the strokes of the valve plungers. Because of the earlier-mentioned additional control function of the valve plungers, however, these devices have not met with success, due to operational difficulties connected with said control function of the valve plungers during cycling. Consequently, it is generally accepted that the strokes of the valve plungers should remain constant and should not be made adjustable for increasing or decreasing the amount of lubricant supplied to the branch lines.
A known adjustable progressive distributor valve is described in German Pat. No. 1,625,894. In this device, several valve plungers operate in a cycling operation, moving over fixed strokes, under the action of a pressurized supply of lubricant. Each plunger has a central axial bore therethrough, inside which is arranged a metering plunger which is movable relative to the surrounding valve plunger. This metering plunger has an adjustable stroke determined by abutment members which are adjustable independently of the stroke of the valve plunger. A resetting of these abutment members thus produces a corresponding change in the volume of lubricant discharged during each valve plunger movement, by changing the stroke of the central metering plunger.
A shortcoming of the above prior art device relates to the fact that an adjustment of the stroke of the central metering plunger affects both branch lines fed by the valve plunger in the same way. For many practical applications, however, this simultaneous adjustment of two branch lines is undesirable, because of conditions which require that each line be adjustable independently of all other branch lines. A compromise solution of the kind offered in the above prior art device may then necessitate the supply of excess lubricant to some branch lines, in order to have an adequate supply to other branch lines. Additional difficulties may arise in a situation, where volume adjustments on a particular line are necessary under changing operating conditions, which adjustments then may necessitate the undoing of optimal volume adjustments for associated branch lines.